Lubricant oil composition for spark ignition type internal combustion engine, method for producing lubricant oil composition, spark ignition type internal combustion engine using lubricant oil composition, and method for lubricating internal combustion engine

ABSTRACT

Provided are a lubricating oil composition for internal combustion engine capable of preventing a deterioration of the combustion state of a spark-ignition internal combustion engine, specifically, a lubricating oil composition to be used for a spark-ignition internal combustion engine in which a total tension per piston of tensions applied to the piston ring is 100 N or less, the lubricating oil composition being a lubricating oil composition including a base oil, (A) a calcium-based detergent, at least one selected from (B1) a sodium-based additive and (B2) a magnesium-based additive, and (C) an ash-free sulfur-based additive in predetermined contents; a method for producing the lubricating oil composition; a spark-ignition internal combustion engine using the lubricating oil composition; and a method for lubricating the internal combustion engine.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition forspark-ignition internal combustion engine, a method for producing thelubricating oil composition, a spark-ignition internal combustion engineusing the lubricating oil composition, and a method for lubricating theinternal combustion engine.

BACKGROUND ART

In view of increasing awareness of environmental issues, an improvementof fuel consumption performance of automobiles having an internalcombustion engine, or the like is being demanded. As an example of theimprovement of fuel consumption performance, there is known a method ofreducing a friction loss to be caused due to friction between a pistonring and a cylinder inner wall of an internal combustion engine (see PTL1). According to this method, the friction loss is reduced by reducing atension applied to the piston ring.

Meanwhile, the fuel consumption performance may also be improved bysetting a viscosity of a lubricating oil composition to be used for aninternal combustion engine low.

CITATION LIST Patent Literature

PTL 1: JP 2012-215238A

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a constitutional view explaining a spark-ignition internalcombustion engine 1 according to an embodiment of the present invention.

SUMMARY OF INVENTION Technical Problem

However, if the piston ring tension is excessively reduced, so-calledoil loss through piston, in which the lubricating oil compositioninvades into a combustion chamber, is liable to be generated. Inaddition, even in the case of using a low-viscosity lubricating oilcomposition, similarly in view of the facts that a flow resistance issmall and that a permeation amount in an oil ring increases, oil lossthrough piston is liable to be generated.

The lubricating oil composition which has invaded into the combustionchamber due to the oil loss through piston is exposed to high heat, abase oil evaporates, and a metal-based additive blended in thelubricating oil composition is concentrated. In order to improvedetergency of the lubricating oil composition, for example, acalcium-based detergent is added as the metal-based additive. However,it may be considered that if this metal-based additive is concentrated,a deterioration of the combustion state is caused, resulting in causingknocking.

Then, even in a spark-ignition internal combustion engine in which oilloss through piston is liable to be generated, upon determining anadditive and an amount thereof for a good combustion state, and itsaddition amount, an object of the present invention is to provide alubricating oil composition for spark-ignition internal combustionengine, which has excellent detergency, a method for producing thelubricating oil composition, a spark-ignition internal combustion engineusing the lubricating oil composition, and a method for lubricating theinternal combustion engine.

Solution to Problem

The present inventors have found that according to a lubricating oilcomposition having the following constitution, even if the oil lossthrough piston is generated, not only the combustion state is madefavorable, but also excellent detergency is obtained.

The present invention provides the following.

[1] A lubricating oil composition for spark-ignition internal combustionengine that is a lubricating oil composition to be used for aspark-ignition internal combustion engine in which a total tension perpiston of tensions applied to the piston ring is 100 N or less, thelubricating oil composition being a lubricating oil compositionincluding a base oil, (A) a calcium-based detergent, at least oneselected from (B1) a sodium-based additive and (B2) a magnesium-basedadditive, and (C) an ash-free sulfur-based additive, wherein the contentof the component (A) as expressed in terms of a calcium atom is 0.15% bymass or less on a basis of the total amount of the lubricating oilcomposition; a sum total of the content of the component (B1) asexpressed in terms of a sodium atom and the content of the component(B2) as expressed in terms of a magnesium atom is 0.2% by mass or lesson a basis of the total amount of the lubricating oil composition; andthe content of the component (C) as expressed in terms of a sulfur atomis 0.01% by mass or more on a basis of the total amount of thelubricating oil composition.[2] A method for producing a lubricating oil composition forspark-ignition internal combustion engine that is a lubricating oilcomposition to be used for a spark-ignition internal combustion enginein which a total tension per piston of tensions applied to the pistonring is 100 N or less, the method including blending a base oil with (A)a calcium-based detergent, at least one selected from (B1) asodium-based additive and (B2) a magnesium-based additive, and (C) anash-free sulfur-based additive in such a manner that the content of thecomponent (A) as expressed in terms of a calcium atom is 0.15% by massor less on a basis of the total amount of the lubricating oilcomposition; a sum total of the content of the component (B1) asexpressed in terms of a sodium atom and the content of the component(B2) as expressed in terms of a magnesium atom is 0.2% by mass or lesson a basis of the total amount of the lubricating oil composition; andthe content of the component (C) as expressed in terms of a sulfur atomis 0.01% by mass or more on a basis of the total amount of thelubricating oil composition.[3] A spark-ignition internal combustion engine in which a total tensionper piston of tensions applied to the piston ring is 100 N or less, thespark-ignition internal combustion engine including using a lubricatingoil composition including a base oil, (A) a calcium-based detergent, atleast one selected from (B1) a sodium-based additive and (B2) amagnesium-based additive, and (C) an ash-free sulfur-based additive,wherein the content of the component (A) as expressed in terms of acalcium atom is 0.15% by mass or less on a basis of the total amount ofthe lubricating oil composition; a sum total of the content of thecomponent (B1) as expressed in terms of a sodium atom and the content ofthe component (B2) as expressed in terms of a magnesium atom is 0.2% bymass or less on a basis of the total amount of the lubricating oilcomposition; and the content of the component (C) as expressed in termsof a sulfur atom is 0.01% by mass or more on a basis of the total amountof the lubricating oil composition.[4] A method for lubricating a spark-ignition internal combustion enginein which a total tension per piston of tensions applied to the pistonring is 100 N or less, the method including undergoing lubrication usinga lubricating oil composition including a base oil, (A) a calcium-baseddetergent, at least one selected from (B1) a sodium-based additive and(B2) a magnesium-based additive, and (C) an ash-free sulfur-basedadditive, wherein the content of the component (A) as expressed in termsof a calcium atom is 0.15% by mass or less on a basis of the totalamount of the lubricating oil composition; a sum total of the content ofthe component (B1) as expressed in terms of a sodium atom and thecontent of the component (B2) as expressed in terms of a magnesium atomis 0.2% by mass or less on a basis of the total amount of thelubricating oil composition; and the content of the component (C) asexpressed in terms of a sulfur atom is 0.01% by mass or more on a basisof the total amount of the lubricating oil composition.

Advantageous Effects of Invention

In accordance with the present invention, it is possible to provide alubricating oil composition for internal combustion engine, in whicheven if the oil loss through piston is generated, not only thecombustion state is made favorable, but also excellent detergency isrevealed, a method for producing the lubricating oil composition, aspark-ignition internal combustion engine using the lubricating oilcomposition, and a method for lubricating the internal combustionengine.

DESCRIPTION OF EMBODIMENTS

The present invention is hereunder described in more detail.

[Lubricating Oil Composition for Spark-Ignition Internal CombustionEngine]

The lubricating oil composition for spark-ignition internal combustionengine according to an embodiment of the present invention is alubricating oil composition including a base oil, (A) a calcium-baseddetergent, at least one selected from (B1) a sodium-based additive and(B2) a magnesium-based additive, and (C) an ash-free sulfur-basedadditive, wherein the content of the component (A) as expressed in termsof a calcium atom is 0.15% by mass or less on a basis of the totalamount of the lubricating oil composition; a sum total of the content ofthe component (B1) as expressed in terms of a sodium atom and thecontent of the component (B2) as expressed in terms of a magnesium atomis 0.2% by mass or less on a basis of the total amount of thelubricating oil composition; and the content of the component (C) asexpressed in terms of a sulfur atom is 0.01% by mass or more on a basisof the total amount of the lubricating oil composition.

<Base Oil>

As the base oil which is used in the lubricating oil compositionaccording to an embodiment of the present invention, an arbitrarymaterial may be properly selected and used among mineral oils andsynthetic oils which have been conventionally used as the base oil oflubricating oil for internal combustion engine.

Examples of the mineral oil may include distillates obtained throughatmospheric distillation of paraffin-base crude oil, intermediate-basecrude oil, or naphthene-base crude oil, or distillates obtained throughvacuum distillation of a residual oil of atmospheric distillation, orrefined oils obtained through refining of such a distillate according toa conventional method, for example, solvent refined oil, hydrogenatedrefined oil, dewaxing treated oil, white clay treated oil, etc.

Examples of the synthetic oil include poly-α-olefins (PAO), such aspolybutene, homopolymers or copolymers of an α-olefin (for example,homopolymers or copolymers of an α-olefin having 8 to 14 carbon atoms,e.g., an ethylene-α-olefin copolymer, etc.), etc.; various esters, suchas polyol esters, dibasic acid esters, phosphate esters, etc.; variousethers, such as polyphenyl ether, etc.; polyglycols; alkylbenzenes;alkylnaphthalenes; synthetic oils obtained through isomerization of awax (GTL wax) produced by the Fischer-Tropsch process, etc.; and thelike.

In the present invention, as the base oil, a single kind of each of theaforementioned mineral oils and synthetic oils may be used, or acombination of two or more kinds thereof may be used. In addition, amixture of the mineral oil and the synthetic oil may also be used.

Although a viscosity of the base oil may be properly determinedaccording to an application of the lubricating oil composition, thekinematic viscosity at 100° C. is generally 2 mm²/s or more and 30 mm²/sor less, preferably 2 mm²/s or more and 15 mm²/s or less, and morepreferably 2 mm²/s or more and 10 mm²/s or less. When the kinematicviscosity at 100° C. is 2 mm²/s or more, an evaporation loss is small;whereas when it is 30 mm²/s or less, a power loss to be caused due toviscous resistance is not so large, and hence, a fuel consumptionimproving effect is obtained.

As for the base oil, its viscosity index is generally 80 or more,preferably 100 or more, and more preferably 120 or more. The base oilhaving a viscosity index of 80 or more is small in a change of viscosityto be caused due to a change of temperature, and hence, it is preferred.

In the case of using, as the base oil, a mixture of mineral oils, amixture of synthetic oils, or a mixture of a mineral oil and a syntheticoil, the viscosity after mixing has only to fall within theaforementioned range. As an example, the base oil containing a mineraloil having a viscosity index of 120 or more which is corresponding toGroup 3 of the API classification and/or a poly-α-olefin (PAO) may beused.

It is to be noted that the content of the base oil on a basis of thetotal amount of the lubricating oil composition for spark-ignitioninternal combustion engine is preferably 60% by mass or more, morepreferably 70% by mass or more, and still more preferably 80% by mass ormore. In addition, an upper limit of the content is preferably 99% bymass, and more preferably 95% by mass or less.

<(A) Calcium-Based Detergent>

Examples of the calcium-based detergent (A) which is used in thelubricating oil composition according to an embodiment of the presentinvention include calcium salts of a sulfonate, a phenate, and asalicylate. These may be used alone or in combination of plural kindsthereof. From the viewpoint of detergency, a calcium salt of salicylate(calcium salicylate) is preferred.

The calcium salt of sulfonate has a molecular weight of preferably 300to 1,500, and more preferably 400 to 700. Calcium salts of an alkylaromatic sulfonic acid obtained through sulfonation of an alkyl aromaticcompound are preferably used.

As the phenate, calcium salts of an alkylphenol, an alkylphenol sulfide,or a Mannich reaction product of an alkylphenol are preferably used.

As the salicylate, calcium salts of an alkylsalicylic acid arepreferably used.

The alkyl group constituting the calcium-based detergent is an alkylgroup having preferably 4 to 30 carbon atoms, and more preferably 6 to18 carbon atoms, and the alkyl group may be either linear or branched.The alkyl group may be a primary alkyl group, a secondary alkyl group,or a tertiary alkyl group.

Examples of the calcium salts of a sulfonate, a phenate, and asalicylate include not only a neutral calcium-based detergent, such as aneutral calcium sulfonate, a neutral calcium phenate, and a neutralcalcium salicylate, each of which is obtained by allowing theaforementioned alkyl aromatic sulfonic acid, alkylphenol, alkylphenolsulfide, Mannich reaction product of an alkylphenol, or alkylsalicylicacid, or the like to react directly with a calcium salt base, such as anoxide or hydroxide, etc., of calcium, or once forming into an alkalimetal salt, such as a sodium salt, a potassium salt, etc., and thensubstituting with a calcium salt, or other means; but also a basiccalcium-based detergent, such as a basic calcium sulfonate, a basiccalcium phenate, and a basic calcium salicylate, each of which isobtained by heating a neutral calcium-based detergent and an excess of acalcium salt or a calcium base in the presence of water, etc., as wellas an overbased calcium-based detergent, such as an overbased calciumsulfonate, an overbased calcium phenate, and an overbased calciumsalicylate, each of which is obtained by allowing a neutral calciumsulfonate, a neutral calcium phenate, or a neutral calcium salicylate toreact with a carbonate or borate of calcium in the presence of a carbondioxide gas, etc.

As for a metal ratio of the calcium-based detergent, a material having ametal ratio of generally 20 or less may be used alone or in admixture oftwo or more thereof.

It is to be noted that the metal ratio as referred to herein isexpressed by (valence of metal element)×(metal element content (mol%))/(soap group content (mol %)) in the metal-based detergent (in thiscase, the calcium-based detergent); the metal element as referred toherein means calcium; and the soap group as referred to herein means asulfonic acid group, a phenol group, a salicylic acid group, or thelike.

From the viewpoint of detergency, the content of the calcium atomcontained in the calcium-based detergent is preferably 1 to 20% by mass,more preferably 2 to 15% by mass, and still more preferably 3 to 10% bymass.

From the viewpoints of detergency and acid neutralization performance, abase number of the calcium-based detergent is preferably 10 to 600mgKOH/g, more preferably 50 to 300 mgKOH/g, and still more preferably100 to 250 mgKOH/g.

It is to be noted that the base number as referred to herein means abase number as measured by the hydrochloric acid method in conformitywith JIS K2501, the 7th section of “Petroleum products and lubricatingoils-neutralization number test method”.

The content of the calcium-based detergent (A) as expressed in terms ofa calcium atom is 0.15% by mass or less on a basis of the total amountof the lubricating oil composition. When the content of the component(A) is 0.15% by mass or less, even if the oil loss through piston isgenerated, the combustion state may be made favorable. From the sameviewpoint and also taking into consideration detergency and fuelconsumption performance, the content of the component (A) is preferably0.05 to 0.15% by mass, more preferably 0.06 to 0.15% by mass, and stillmore preferably 0.08 to 0.15% by mass.

<(31) Sodium-Based Additive>

The lubricating oil composition according to an embodiment of thepresent invention contains at least one selected from (B1) asodium-based additive and (B2) a magnesium-based additive.

As the sodium-based additive (B1) which is used in the presentinvention, for example, a sodium-based detergent is preferablyexemplified. Examples of the sodium-based detergent include sodium saltsof a sulfonate, a phenate, and a salicylate. These may be used alone orin combination of plural kinds thereof. From the viewpoint ofdetergency, a sodium salt of sulfonate (sodium sulfonate) is preferred.

With respect to the aforementioned sodium-based detergent, thesulfonate, phenate, and salicylate are the same as in the explanation ofthe sulfonate, phenate, and salicylate for the aforementionedcalcium-based detergent. In addition, the matter that a basicsodium-based detergent and an overbased sodium-based detergent may beadopted is the same as in the explanation for the calcium-baseddetergent.

From the viewpoint of detergency the content of the sodium atomcontained in the sodium-based detergent is preferably 1 to 25% by mass,more preferably 5 to 25% by mass, and still more preferably 10 to 20% bymass.

From the viewpoints of detergency and acid neutralization performance, abase number of the sodium-based detergent is preferably 10 to 650mgKOH/g, more preferably 100 to 600 mgKOH/g, and still more preferably300 to 550 mgKOH/g.

<(B2) Magnesium-Based Additive>

As the magnesium-based additive (B2) which is used in the lubricatingoil composition according to an embodiment of the present invention, forexample, a magnesium-based detergent is preferably exemplified. Examplesof the magnesium-based detergent include magnesium salts of a sulfonate,a phenate, and a salicylate. These may be used alone or in combinationof plural kinds thereof. From the viewpoint of detergency, a magnesiumsalt of salicylate (magnesium salicylate) is preferred.

With respect to the aforementioned magnesium-based detergent, thesulfonate, phenate, and salicylate are the same as in the explanation ofthe sulfonate, phenate, and salicylate for the aforementionedcalcium-based detergent. In addition, the matter that a basicmagnesium-based detergent and an overbased magnesium-based detergent maybe adopted is the same as in the explanation for the calcium-baseddetergent.

From the viewpoint of detergency, the content of the magnesium atomcontained in the magnesium-based detergent is preferably 1 to 25% bymass, more preferably 2 to 20% by mass, and still more preferably 5 to20% by mass.

From the viewpoints of detergency and acid neutralization performance, abase number of the magnesium-based detergent is preferably 10 to 650mgKOH/g, more preferably 100 to 600 mgKOH/g, and still more preferably200 to 550 mgKOH/g.

<Contents of Components (A), (B1), and (B2)>

The lubricating oil composition according to an embodiment of thepresent invention contains at least one selected from (B) a sodium-basedadditive and (B2) a magnesium-based additive in the content of a sumtotal of the content as expressed in terms of a sodium atom and thecontent as expressed in terms of a magnesium atom of 0.2% by mass orless on a basis of the total amount of the lubricating oil composition.When the content falls within the aforementioned range, excellentdetergency is obtained, and the combustion state may be made favorable.From the same viewpoints, the content of a sum total of the content asexpressed in terms of a sodium atom and the content as expressed interms of a magnesium atom is preferably 0.005 to 0.20% by mass, morepreferably 0.01 to 0.15% by mass, and still more preferably 0.01 to0.10% by mass.

As for the relation of the calcium-based detergent (A) with thesodium-based additive (BR) and the magnesium-based additive (B2), a massratio of the magnesium atom (Mg) contained in the magnesium-basedadditive and/or the sodium atom (Na) contained in the sodium-basedadditive to the calcium atom (Ca) [(Mg and/or Na)/Ca] is preferably 0.03to 3.5. When the content of the calcium-based detergent (A) and thecontents of the sodium-based additive (B1) and the magnesium-basedadditive (B2) satisfy the aforementioned relation, excellent detergencyis obtained, and the combustion state may be made favorable. From thesame viewpoints, the mass ratio of the magnesium atom (Mg) and/or thesodium atom (Na) to the calcium atom (Ca) [(Mg and/or Na)/Ca] ispreferably 0.05 to 2.5, more preferably 0.05 to 1, and still morepreferably 0.06 to 0.8.

<(C) Ash-Free Sulfur-Based Additive>

The lubricating oil composition according to an embodiment of thepresent invention contains (C) an ash-free sulfurbased additive.

The ash-free sulfurbased additive (C) is not particularly limited solong as it is an additive containing sulfur but not containing a metalatom. Examples thereof include sulfur-containing amine-based additives,such as a thiazine, a dithiazine, an imidazolethione, animidazoledithione, a thiazole, a dithiazole, a thiadiazole, adithiadiazole, a dithiocarbamate, etc.; aromatic mercaptan-basedadditives, such as a thiocresol, a dithiocresol, a thiophenol, adithiophenol, etc.; thiopropionate-based additives, such as athiopropionate, a dithiopropionate, a thiodipropionate, adithiodipropionate, etc.; and those known as an antioxidant, an oxygenscavenger, an anti-wear agent, an extreme pressure agent, or the like,such as a sulfurized fat and oil, a sulfide, a disulfide, a sulfonicacid, a sulfur-containing phenol, etc. These may be used alone or incombination of plural kinds thereof.

As other ash-free sulfur-based additives than those described above,there are also preferably exemplified additives chiefly used as ananti-wear agent, having a structure in which a heterocyclic ringcontaining sulfur, for example, a sulfur-containing heterocyclic ring,such as a benzothiophene ring, a naphthothiophene ring, adibenzothiophene ring, a thienothiophene ring, a dithienobenzene ring, athiophene ring, a naphthothiazole ring, an isothiazole ring, anaphthoisothiazole ring, a phenothiazine ring, a phenoxathine ring, adithianaphthalene ring, a thianthrene ring, a thioxanthene ring, abithiophene ring, etc., is included, and at least one sulfur atom isbonded to the carbon atom of the heterocyclic ring.

Among these, dithiocarbamates, such as dialkyl dithiocarbamates having alinear or branched alkyl group having 1 to 20 carbon atoms, etc.;thiopropionates, such as dialkyl thiopropionates having a linear orbranched alkyl group having 1 to 20 carbon atoms, for example, didodecylthiopropionate, dioctadecyl thiopropionate, dimyristyl thiopropionate,dodecyloctadecyl thiopropionate, etc., etc.; thiodipropionates, such asdialkyl thiodipropionates corresponding to the foregoingthiopropionates, etc.; thiazoles, such as alkyl thiazoles, aminoalkylthiazoles, alkyl benzothiazoles, and alkyl mercaptothiazoles, eachhaving a linear or branched alkyl group having 1 to 20 carbon atoms,aminothiazole, benzothiazole, etc.; sulfides, such as benzyl sulfides,for example, bis(3-methyl-4-hydroxy-5-t-butylbenzyl)sulfide, etc.,hydroxybenzyl sulfides, for example,tetraphthaloyl-di(2,6-dimethyl-4-t-butyl-3-hydroxybenzylsulfide), etc.,dialkyl sulfides having a linear or branched alkyl group having 1 to 20carbon atoms, for example, didodecyl sulfide, dioctadecyl sulfide, etc.,etc.; disulfides corresponding to the aforementioned sulfides; andsulfur-containing phenols having a phenol group which may be substitutedwith at least a linear or branched alkyl group having 1 to 20 carbonatoms and which may have, together with the foregoing phenol group, anitrogen-containing organic group or nitrogen-containing heterocyclicgroup, such as an amino group, an imino group, an amide group, an imidegroup, a pyridyl group, a pyrazine group, a triazine group, abenzimidazole group, etc., or a linear or branched alkyl group having 1to 20 carbon atoms, such groups being optionally connected with eachother via a divalent organic group, such as an alkylene group, acycloalkylene group, an alkenylene group, an arylene group, etc., —NH—,—O—, —S—, —COO—, etc., for example,2,2′-thiobis-(6-t-butyl-4-methylphenol),4,4′-[thiobis(ethyleneoxycarbonylethylene)]bis(2,6-di-t-butylphenol),tridecyl-3,5-di-t-butyl-4-hydroxybenzyl thioacetate,2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,6-triazin-2-ylamino)phenol,2-octylthio-4,6-di(3,5-di-t-butyl-4-hydroxyphenoxy)-s-triazine, etc.,are preferred. As described above, the ash-free sulfur-based additivewhich is used in the present invention may or may not have a cyclicstructure in a molecule thereof and may or may not have a hetero ringcontaining sulfur.

Though the content of the sulfur atom contained in the ash-freesulfur-based additive varies with the additive to be used, it isgenerally 1 to 40% by mass, and preferably 3 to 35% by mass. Inaddition, with respect to the thiopropionate-based additive, thesulfide, or the disulfide, the content of the sulfur atom is morepreferably 3 to 15% by mass. When the content of the sulfur atom fallswithin the aforementioned range, not only the combustion state may bemade favorable, but also excellent detergency and fuel consumptionperformance are obtained.

The content of the ash-free sulfur-containing additive (C) as expressedin terms of a sulfur atom is 0.01% by mass or more on a basis of thetotal amount of the lubricating oil composition. When the content of thecomponent (C) is less than 0.01% by mass, the detergency is notobtained, and the combustion state may not be made favorable. From thesame viewpoints, the content of the component (C) as expressed in termsof a sulfur atom is preferably 0.01 to 3% by mass, more preferably 0.03to 1% by mass, and still more preferably 0.03 to 0.5% by mass.

<(D) Organic Molybdenum-Based Additive>

The lubricating oil composition according to an embodiment of thepresent invention may contain (D) an organic molybdenum-based additive.As the organic molybdenum-based additive, for example, amolybdenum-based friction modifier and a molybdenum-based antioxidantmay be used.

As the molybdenum-based friction modifier, all of arbitrary compoundswhich are generally used as a friction modifier of lubricating oil forinternal combustion engine may be used. For example, there isexemplified at least one selected from a molybdenum amine complex and/oroxymolybdenum dithiocarbamate sulfide, a trinuclear molybdenum-sulfurcompound, and molybdenum dithiophosphate. More specifically, at leastone selected from molybdenum dithiocarbamate (MoDTC), molybdenumdithiophosphate (MoDTP), and an amine salt of molybdic acid may be used.

As the molybdenum-based antioxidant, there is preferably exemplified amolybdenum amine complex. As the molybdenum amine complex, hexavalentmolybdenum compounds, specifically those obtained through a reaction ofmolybdenum trioxide and/or molybdic acid with an amine compound, forexample, compounds obtained by the production method described in JP2003-252887A, may be used.

As for a reaction ratio of the hexavalent molybdenum compound to theamine compound, a molar ratio of the Mo atom of the molybdenum compoundis preferably 0.7 to 5, more preferably 0.8 to 4, and still morepreferably 1 to 2.5 relative to one mole of the amine compound. As for areaction method, a conventionally known method, for example, a methoddescribed in JP 2003-252887A, may be adopted.

In the present invention, as the molybdenum-based antioxidant, besidesthe aforementioned molybdenum amine complex, a sulfur-containingmolybdenum complex of succinimide, as described in JP 3-22438B, JP2004-2866A, etc., may also be used.

In the present invention, from the viewpoint of fuel consumptionperformance, the component (D) is preferably a molybdenum-based frictionmodifier. Above all, at least one selected from molybdenumdithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and anamine salt of molybdic acid is preferred, and molybdenum dithiocarbamate(MoDTC) is especially preferred.

The content of the component (D) is preferably 0.05 to 5% by mass, morepreferably 0.1 to 3% by mass, and still more preferably 0.3 to 1.5% bymass on a basis of the total amount of the lubricating oil composition.In addition, the content of the component (D) as expressed in terms of amolybdenum atom is preferably 0.005 to 0.20% by mass on a basis of thetotal amount of the lubricating oil composition. From the viewpoint ofmaintaining the wear resistant properties, the content of the component(D) is more preferably 0.01 to 0.15% by mass, and still more preferably0.03 to 0.15% by mass.

<Additives>

In the lubricating oil composition according to the embodiment of thepresent invention, it is preferred to further contain at least oneadditive selected from a viscosity index improver, a dispersant, anextreme pressure agent, a non-sulfur-based antioxidant, and a defoamingagent.

(Viscosity Index Improver)

Examples of the viscosity index improver include a poly(meth)acrylate (adispersion type and a non-dispersion type), an olefin-based copolymer(for example, an ethylene-propylene copolymer, etc.), a dispersion typeolefin-based copolymer, a styrene-based copolymer (for example, astyrene-diene copolymer, a styrene-isoprene copolymer, etc.), and thelike. Above all, a poly(meth)acrylate is preferred.

A weight average molecular weight (Mw) of such a viscosity indeximprover is preferably 10,000 to 1,000,000, more preferably 30,000 to600,000, and still more preferably 100,000 to 600,000. When themolecular weight falls within the aforementioned range, an excellentfuel consumption performance is obtained. Here, the weight averagemolecular weight is a value as measured by means of GPC and obtainedwhile making polystyrene as a calibration curve, and in detail, it ismeasured under the following condition.

Column: Two of TSK gel GMH6

Measurement temperature: 40° C.

Sample solution: 0.5% by mass THF solution

Detection device: Refractive index detector

Standard: Polystyrene

A blending amount of such a viscosity index improver may be properlydetermined according to a desired viscosity (for example, HTHS viscosityat 150° C.), and from the standpoint of a blending effect, it ispreferably 0.01 to 10.00% by mass, more preferably 0.05 to 5.00% bymass, and still more preferably 0.05 to 2.00% by mass on a basis of thelubricating oil composition.

Here, the content of the poly(meth)acrylate means the content of onlythe resin component composed of a poly(meth)acrylate and is the contenton a basis of the solid component in which a mass of, for example, adiluent oil, etc. contained together with the poly(meth)acrylate is notincluded.

(Dispersant)

As the dispersant, a non-boronated imide-based dispersant may be used.The non-boronated imide-based dispersant is one generally called animide-based dispersant. As such an imide-based dispersant, it issuitable to use a succinimide. Examples of the succinimide includecompounds of a mono-type represented by the following general formula(1) and a bis-type represented by the following general formula (2).

In the aforementioned general formulae (1) and (2), R¹, R³, and R⁴ areeach an alkenyl group or alkyl group having a number average molecularweight of 500 to 4,000, and R³ and R⁴ may be the same as or differentfrom each other. The number average molecular weight of each of R¹, R³,and R⁴ is preferably 1,000 to 4,000.

When the number average molecular weight of each of R¹, R³, and R⁴ is500 or more, the solubility in the base oil is favorable, and when it is4,000 or less, favorable dispersibility is obtained, and excellentdetergency is obtained.

R², R⁵, and R⁶ are each an alkylene group having 2 to 5 carbon atoms,and R⁵ and R⁶ may be the same as or different from each other.

m is an integer of 1 to 10, preferably an integer of 2 to 5, and morepreferably 3 or 4. When m is 1 or more, the dispersibility is favorable,and when it is 10 or less, the solubility in the base oil is favorable,and excellent detergency is obtained. In addition, n is an integer of 0to 10, preferably an integer of 1 to 4, and more preferably 2 or 3. Whenn falls within the aforementioned range, such is preferred from thestandpoints of dispersibility and solubility in the base oil, andexcellent detergency is obtained.

In general, the succinimide may be produced by allowing analkenylsuccinic anhydride obtained through a reaction of a polyolefinwith maleic anhydride, or an alkylsuccinic anhydride obtained throughhydrogenation of the alkenylsuccinic anhydride, to react with apolyamine. In addition, the succinimide compound of a mono-type and thesuccinimide compound of a bis-type may be produced by altering areaction ratio of the alkenylsuccinic anhydride or alkylsuccinicanhydride to the polyamine,

Examples of the polyamine may include single diamines, such asethylenediamine, propylenediamine, butylenediamine, etc.;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine,di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine,etc.; and piperazine derivatives, such as aminoethylpiperazine, etc.

Taking into consideration the detergency, the content of the succinimideis preferably 0.1 to 10% by mass, more preferably 0.3 to 8% by mass, andstill more preferably 0.5 to 5% by mass on a basis of the total amountof the lubricating oil composition; and the content of the succinimideas expressed in terms of a nitrogen atom is preferably 0.005 to 0.3% bymass, and more preferably 0.01 to 0.1% by mass on a basis of the totalamount of the lubricating oil composition.

A boronated succinimide may be, for example, produced by allowing theaforementioned alkenylsuccinic anhydride obtained through a reaction ofa polyolefin with maleic anhydride, or the alkylsuccinic anhydride, toreact with the aforementioned polyamine and a boron compound.

Examples of the boron compound include boron oxide, a boron halide,boric acid, boric anhydride, a boric acid ester, an ammonium salt ofboric acid, and the like.

It is to be noted that a mass ratio of the boron content B to thenitrogen content N (B/N) in the boronated succinimide is generally 0.1to 3, and preferably 0.2 to 1.

Taking into consideration the detergency, the content of the boronatedsuccinimide is preferably 0.1 to 10% by mass, more preferably 0.3 to 8%by mass, and still more preferably 0.5 to 5% by mass on a basis of thetotal amount of the lubricating oil composition; and the content of theboronated succinimide as expressed in terms of a boron atom ispreferably 0.005 to 0.3% by mass, and more preferably 0.01 to 0.1% bymass on a basis of the total amount of the lubricating oil composition.

In the lubricating oil composition of the present invention, a modifiedpolybutenyl succinimide obtained by allowing the aforementionedsuccinimide to react with an alcohol, an aldehyde, a ketone, analkylphenol, a cyclic carbonate, an epoxy compound, an organic acid, orthe like may also be used.

(Anti-Wear Agent)

As the anti-wear agent, for example, a zinc dithiophosphate representedby the following general formula (3), such as a zincdialkyldithiophosphate, a zinc dialkyldioxyphosphate, etc., ispreferably exemplified.

In the aforementioned general formula (3), Xs are each independently anoxygen atom or a sulfur atom, and at least two of them are the sameatom; and R, and R# are each independently a primary or secondary alkylgroup having 3 to 22 carbon atoms or an alkylaryl group substituted withan alkyl group having 3 to 18 carbon atoms.

Here, examples of the primary or secondary alkyl group having 3 to 22carbon atoms include a propyl group, a butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a nonyl group, a decylgroup, a dodecyl group, a tetradecyl group, a hexadecyl group, anoctadecyl group, and an eicosyl group, each of which is primary orsecondary, and the like. In addition, examples of the alkylaryl groupsubstituted with an alkyl group having 3 to 18 carbon atoms include apropylphenyl group, a pentylphenyl group, an octylphenyl group, anonylphenyl group, a dodecylphenyl group, and the like.

In the present invention, the aforementioned zinc dithiophosphate may beused alone or in combination of plural kinds thereof, however, from theviewpoint of enhancing the wear resistant properties, it is especiallypreferred to use a zinc dithiophosphate of a secondary alkyl group.

As the anti-wear agent, other anti-war agent than the aforementioneddithiophosphoric acid, such as an ash-free friction modifier, e.g., analiphatic amine, a fatty acid ester, a fatty acid amide, a fatty acid,an aliphatic alcohol, an aliphatic ether, etc., etc., may also be used.

The content of the anti-wear agent is preferably 0.1 to 10% by mass, andmore preferably 0.3 to 5% by mass on a basis of the total amount of thelubricating oil composition. In addition, in the case of using a zincdithiophosphate as the anti-wear agent, the content of the zincdithiophosphate as expressed in terms of a phosphorus atom is preferably0.005 to 0.2% by mass, and more preferably 0.01 to 0.15% by mass on abasis of the total amount of the composition.

(Extreme Pressure Agent)

Examples of the extreme pressure agent include thiophosphoric acidester-based extreme pressure agents, such as a trialkyltrithiophosphate, a triaryl trithiophosphate, a triaralkyltrithiophosphate, etc.; phosphorus-based extreme pressure agents, suchas phosphoric acid esters or phosphorous acid esters, e.g., a trialkylphosphate, a triaryl phosphate, a trialkyl phosphonate, a trialkylphosphite, a triaryl phosphite, a dialkyl hydrogenphosphite, etc., oramine salts thereof, etc.; organic metal-based extreme pressure agents,such as alkali metal salts or alkaline earth metal salts of a carboxylicacid or dicarboxylic acid having 3 to 60 carbon atoms; and the like.These may be used alone or in combination of plural kinds thereof.

From the viewpoints of lubricity and stability, the content of theextreme pressure agent is preferably 0.001 to 5% by mass, and morepreferably 0.005 to 3% by mass on a basis of the total amount of thelubricating oil composition.

(Non-Sulfur-Based Antioxidant)

As the non-sulfur-based antioxidant, a molybdenum-based antioxidant, aphenol-based antioxidant, an amine-based antioxidant, and so on may besuitably used.

Examples of the molybdenum-based antioxidant include molybdenum aminecomplexes obtained through a reaction of molybdenum trioxide and/ormolybdic acid with an amine compound; and the like.

As the phenol-based antioxidant, an arbitrary material may be properlyselected and used among known phenol-based antioxidants which have beenconventionally used as the antioxidant of lubricating oil for internalcombustion engine. Examples thereof include monophenol-basedantioxidants, such as alkylphenol-based antioxidants, e.g.,2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, etc., etc.;diphenol-based antioxidants, e.g.,4,4′-methylenebis(2,6-di-t-butylphenol),2,2′-methylenebis(4-ethyl-6-t-butylphenol), etc.; hindered phenol-basedantioxidants; and the like.

As the amine-based antioxidant, an arbitrary material may be properlyselected and used among known amine-based antioxidants which have beenconventionally used as the antioxidant of lubricating oil for internalcombustion engine. Examples thereof include diphenylamine-basedantioxidants, such as diphenylamine, an alkylated diphenylamine havingan alkyl group having 3 to 20 carbon atoms, etc.; naphthylamine-basedantioxidants, such as α-naphthylamine, a phenyl-α-naphthylaminesubstituted with an alkyl group having 3 to 20 carbon atoms, etc.; andthe like.

The non-sulfur-based antioxidant may be used alone or in combination ofplural kinds among those described above.

From the standpoints of a balance between effects and economy, and thelike, the content of the non-sulfur-based antioxidant is preferably 0.05to 7% by mass, and more preferably 0.05 to 5% by mass on a basis of thetotal amount of the lubricating oil composition.

(Defoaming Agent)

Examples of the defoaming agent include a silicone-based defoamingagent, a fluorosilicone-based defoaming agent, a fluoroalkyl ether-baseddefoaming agent, and the like. These may be used alone or in combinationof plural kinds thereof.

From the standpoints of a balance between effects and economy, and thelike, the content of the defoaming agent is preferably 0.005 to 2% bymass, and more preferably 0.01 to 1% by mass on a basis of the totalamount of the lubricating oil composition.

(Other Additives)

In the lubricating oil composition for spark-ignition internalcombustion engine of the present invention, other additive(s) may befurther blended within the range where the purpose of the presentinvention is not impaired, as the need arises.

Examples of the other additive may include a rust inhibitor, such as apetroleum sulfonate, an alkylbenzene sulfonate, dinonylnaphthalenesulfonate, an alkenyl succinate ester, a polyhydric alcohol ester, etc.;an anticorrosive agent; a surfactant, such as a polyalkyleneglycol-based nonionic surfactant, e.g., a polyoxyethylene alkyl ether, apolyoxyethylene alkylphenyl ether, a polyoxyethylene alkylnaphthylether, etc., etc.; a metal deactivator, such as a benzotriazole-basedcompound, a tolyltriazole-based compound, a thiadiazole-based compound,an imidazole-based compound, etc.; a pour point depressant, such as anethylene-vinyl acetate copolymer, a condensate of a chlorinated paraffinand naphthalene, a condensate of a chlorinated paraffin and phenol, apolymethacrylate, a polyalkylstyrene, etc.; an oxygen scavenger, such asan aliphatic unsaturated compound, e.g., an olefin of every sort, adiene, a triene, etc., a terpene having a double bond, etc.; and thelike.

The aforementioned other additive(s) may be properly blended in anamount falling within the range where the purpose of the presentinvention is not impaired.

<Properties of Lubricating Oil Composition for Spark-Ignition InternalCombustion Engine>

A NOACK volatile loss of the lubricating oil composition according tothe embodiment of the present invention is preferably 10% by mass ormore, and more preferably 10 to 15% by mass. When the NOACK volatileloss is 10% by mass or more, a low viscosity sufficient for contributingto the low fuel consumption performance is obtained; and when it is 15%by mass or less, excessive oil loss through piston may be inhibited, andan excellent effect for preventing the deterioration of the combustionstate of the spark-ignition internal combustion engine is obtained.Here, the NOACK volatile loss is a value as measured in conformity withJPI-5S-41-2004.

A kinematic viscosity at 100° C. of the lubricating oil compositionaccording to the embodiment of the present invention is preferably 10mm²/s or less, and more preferably 3 to 10 mm²/s. When the kinematicviscosity is 10 mm²/s or less, a sufficient low fuel consumptionperformance is obtained; and when it is 3 mm²/s or more, excessive oilloss through piston may be inhibited, and an excellent effect forpreventing the deterioration of the combustion state of thespark-ignition internal combustion engine is obtained. Here, thekinematic viscosity at 100° C. is a value as measured in conformity with“Testing methods for kinematic viscosity of petroleum products” asprescribed in JIS K2283.

From the viewpoints that a sufficient low fuel consumption performanceis obtained and that an excellent effect for preventing thedeterioration of the combustion state of the spark-ignition internalcombustion engine is obtained, a sulfated ash content of the lubricatingoil composition according to the embodiment of the present invention ispreferably 1.0% by mass or less, more preferably 0.4 to 1.0% by mass,and still more preferably 0.5 to 1.0% by mass on a basis of the totalamount of the composition. Here, the sulfated ash content is a value asmeasured by the method as prescribed in JIS K2272, the 5^(th) section of“Determination of sulfated ash” of and refers to an ash content obtainedby adding sulfuric acid to a carbonized residue caused by combustion ofa sample and heating so that the residue has a constant mass. Thesulfated ash content is generally used to know a rough amount ofmetal-based additives contained in the lubricating oil composition.

An HTHS viscosity at 150° C. of the lubricating oil compositionaccording to the embodiment of the present invention is preferably 1.0to 5 mPa·s, more preferably 1.0 to 4 mPa·s, and still more preferably1.5 to 3 mPa·s.

When the HTHS viscosity at 150° C. is 1.0 mPa·s or more, the lubricatingperformance may be made favorable; and when it is 5 mPa·s or less, notonly excellent viscosity properties at low temperatures are obtained,but also excellent fuel consumption properties are obtained. The HTHSviscosity at 150° C. may also be assumed as a viscosity in ahigh-temperature region at the time of high-speed operation of anengine. When the HTHS viscosity at 150° C. falls with the aforementionedrange, it may be said that the foregoing lubricating oil composition isfavorable in various properties, such as viscosity in a high-temperatureregion assuming the time of high-speed operation of an engine, etc.

The HTHS viscosity at 150° C. is a value of high temperature high shearviscosity at 150° C. as measured in conformity with ASTM D4741, andspecifically, it is a value obtained by the measurement method asdescribed in the Examples.

<Production Method of Lubricating Oil Composition for Spark-IgnitionInternal Combustion Engine>

The production method of a lubricating oil composition according to theembodiment of the present invention is concerned with a method forproducing a lubricating oil composition for spark-ignition internalcombustion engine that is a lubricating oil composition to be used for aspark-ignition internal combustion engine including a piston having apiston ring, in which a total tension per piston of tensions applied tothe piston ring is 100 N or less, the method including blending a baseoil with (A) a calcium-based detergent, at least one selected from (B1)a sodium-based additive, and (B2) a magnesium-based additive, and (C) anash-free sulfur-based additive in such a manner that the content of thecomponent (A) as expressed in terms of a calcium atom is 0.15% by massor less on a basis of the total amount of the lubricating oilcomposition; a sum total of the content of the component (B1) asexpressed in terms of a sodium atom and the content of the component(B2) as expressed in terms of a magnesium atom is 0.2% by mass or lesson a basis of the total amount of the lubricating oil composition; andthe content of the component (C) as expressed in terms of a sulfur atomis 0.01% by mass or more on a basis of the total amount of thelubricating oil composition.

In producing the lubricating oil composition for spark-ignition internalcombustion engine, at least the aforementioned component (A), component(B1), component (B2), and component (C) have only to be blended withinthe aforementioned content ranges. The organic molybdenum-based additive(D) and at least one selected from a viscosity index improver, adispersant, an anti-wear agent, an extreme pressure agent, anon-sulfur-based antioxidant, and a defoaming agent as well as otheradditive(s) and the like may further be blended within the range wherethe effects of the present invention are not impaired. After separatelymixing the component (A), the component (B1), the component (B2), andthe component (C), and optionally, the component (D) and otheradditive(s), the resulting mixture may be introduced into the base oil,or the respective components may be added to and mixed with the base oilone after another. It is to be noted that the addition order does notmatter.

<Spark-Ignition Internal Combustion Engine and Lubricating Method of theSpark-Ignition Internal Combustion Engine>

A spark-ignition internal combustion engine 1 according to the presentembodiment is described by reference to FIG. 1.

The spark-ignition internal combustion engine 1 in the presentembodiment includes a gasoline engine. Examples of a fuel which is usedfor the spark-ignition internal combustion engine include, in additionto a fuel oil classified into Class I petroleums, petroleum, biomassethanol, an alcohol fuel, a liquefied petroleum gas, a natural gas, asynthetic gas, a hydrogen fuel, a bi-fuel, and the like.

The spark-ignition internal combustion engine 1 includes a cylinderblock 11, a piston crank mechanism 12 installed in the cylinder block11, and a valve mechanism 13 undergoing intake of an air-fuel mixtureinto the cylinder block 11 and exhaust of a combustion gas.

The cylinder block 11 is provided with a cylinder 21 and a crank case22. The spark-ignition internal combustion engine 1 includes a sparkplug F in an upper portion of the cylinder 21. In addition, the pistoncrank mechanism 12 includes a piston 23 and a crank shaft 24. In thepiston 23, a piston ring 30 is disposed. The piston ring 30 isconstituted of a top ring 31, a second ring 32, and an oil ring 33. Inthe spark-ignition internal combustion engine 1, a total tension perpiston of tensions applied to the piston ring 30 is set to 100 N orless.

The total tension per piston of tensions applied to the piston ring 30is a sum total of tensions applied to each of the plural rings. Forexample, in the spark-ignition internal combustion engine 1 shown inFIG. 1, the total tension is a sum total of tensions (n) applied to theeach piston ring of the top ring 31, the second ring 32, and the oilring 33. Here, the tension applied to the piston ring is a value asmeasured in conformity with “Measurement method of tangent tension” ofJIS B8032-2.

The spark-ignition internal combustion engine 1 has a lubricating oilcomposition L. The lubricating oil composition L is stored in an oil pan41 within the crank case 22 or an oil tank (not shown), and followingthe operation of the spark-ignition internal combustion engine 1, thelubricating oil composition L is circulated in the piston crankmechanism 12, the valve mechanism 13, and the like and lubricates andcools each of these parts. In the spark-ignition internal combustionengine 1, the aforementioned lubricating oil composition forspark-ignition internal combustion engine according to the embodiment ofthe present invention is applied as the lubricating oil composition L.

That is, the method for lubricating the spark-ignition internalcombustion engine 1, in which a total tension per piston of tensionsapplied to the piston ring 30 is 100 N or less, with the aforementionedlubricating oil composition for spark-ignition internal combustionengine is included in the present invention.

As mentioned above, in the spark-ignition internal combustion engine inthe present embodiment, the total tension per piston of tensions appliedto the piston ring 30 is 100 N or less. In such a low-tension internalcombustion engine, the oil loss through piston from the crank case 22into a combustion chamber C is liable to be generated. On the otherhand, in the lubricating oil composition for spark-ignition internalcombustion engine according to the present embodiment, even if the oilloss through piston is generated, the generation timing of a cool flamemay be delayed. In addition, so long as the total tension per piston oftensions applied to the piston ring of the spark-ignition internalcombustion engine can be lowered, in the case where the spark-ignitioninternal combustion engine is mounted in an automobile, it is possibleto contemplate to improve the fuel consumption performance of theautomobile. For this reason, the lubricating oil composition forspark-ignition internal combustion engine may be preferably used for alow-tension spark-ignition internal combustion engine, in which a totaltension per piston of tensions applied to the piston ring 30 is 95 N orless, and moreover 90 N or less.

Meanwhile, though a lower limit value of the total tension per piston oftensions applied to the piston ring 30 is not particularly limited, itis preferably 5 N or more, more preferably 10 N or more, and still morepreferably 15 N or more. When the lower limit value is 5 N or more, theoil loss through piston is hardly generated.

EXAMPLES

Next, the present invention is specifically described by reference toExamples, but it should be construed that the present invention is by nomeans limited by these Examples at all. In the following Examples and soon, measurement of properties and performance evaluation of lubricatingoil compositions were carried out in the following manners.

[Evaluation Methods] <Properties of Lubricating Oil Composition>

Respective properties of a base oil, an additive, and a lubricating oilcomposition were measured in the following methods.

(1) Noack Volatile Loss of Lubricating Oil Composition:

The measurement was conducted in conformity with JPI-5S-41-2004.

(2) Kinematic Viscosity:

The kinematic viscosity at each of 40° C. and 100° C. was measured inconformity with “Testing methods for kinematic viscosity of petroleumproducts” as prescribed in JIS K2283-2000.

(3) HTHS Viscosity at 150° C. (High Temperature High Shear Viscosity):

With respect to the objective lubricating oil composition, the viscosityafter shearing at 150° C. and a shear rate of 10⁶/s was measured inconformity with ASTM D4741.

(4) Base Number:

The measurement was conducted by the hydrochloric acid method inconformity with JIS K2501, “Petroleum products and lubricatingoils-neutralization value test method”.

(5) Amounts of Calcium Atom, Sodium Atom, Magnesium Atom, Sulfur Atom,Phosphorus Atom, Boron Atom, and Molybdenum Atom:

The measurement was conducted in conformity with JPI-5S-38-92.

(6) Content of Nitrogen Atom:

The measurement was conducted in conformity with JIS K2609.

<Combustibility Test>

The specification and operating condition of a spark-ignition internalcombustion engine used in the combustibility test are shown below.

(1) Bore diameter: 85 mm(2) Stroke length: 70 mm

(3) Displacement: 397 cm³

(4) Compression ratio: 8/1(5) Number of revolution of engine: 1,400 rpm(6) Air-fuel ratio: Theoretical air-fuel ratio(7) Ignition timing: −5° aTDC

In the aforementioned engine, a small-sized quartz window was providedin a cylinder head, and a light from a xenon light source wastransmitted through a right end portion of a combustion chamber, therebycarrying out light absorption measurement in the end portion. The xenonlight having been transmitted through the combustion chamber wasintroduced into a spectroscope by optical fibers and spectrallyseparated in a wavelength of 293.1 nm. This wavelength is a wavelengthat which strong absorption occurs in formaldehyde. The formaldehyde isan important chemical species such that it is produced at the time ofgeneration of a cool flame and abruptly reduced with the movement into ablue flame and the generation of a hot flame. The spectrally separatedlight was converted into an electric signal by a photomultiplier tube,and by using a transmission light intensity E0 in a state where noreaction takes place and a transmission light intensity E1 at anarbitrary crank angle, an absorbance was defined as (E0−E1)/E0 andcalculated. A timing at which an increase of this absorbance started wasdefined as a generation timing of a cool flame, and a timing at whichthe absorbance abruptly decreased was defined as an autoignition timing.In addition, a pressure sensor was provided within the combustionchamber, and an amplitude of pressure vibration generated at the time ofknocking was measured and defined as an index of the knock intensity.

In an internal combustion engine provided with a reciprocating piston, amixed gas composed of a fuel and an oxidizing agent is compressed by thepiston in a cylinder interior, whereby the temperature and pressureincrease. At this time, before original ignition accompanied by definiteheat generation is generated, the mixed gas ignites itself due to thecompression, thereby causing combustion. This is called low-temperatureautoignition. The low-temperature autoignition includes a stage at whicha low-temperature flame called a cool flame or a blue flame reveals, andan active chemical species is produced, leading to generation andpropagation of a hot flame accompanied by abrupt heat generation.

In a spark-ignition internal combustion engine, an active chemicalspecies is forcedly provided by an ignition source, such as an electricspark, etc., leading to generation and propagation of a hot flame. Forthis reason, in the case where the progress of a low-temperatureautoignition reaction is faster than the generation and propagation of ahot flame originated from the ignition, a deterioration of thecombustion state or abrupt pressure vibration is generated. In view ofthe fact that this abrupt pressure vibration becomes a cause ofknocking, as described above, an amplitude of pressure vibrationgenerated at the time of knocking was measured and defined as an indexof the knock intensity.

After the aforementioned engine was subjected to a warming up operationto set a spark plug washer temperature to 440 to 480K, a sample preparedby blending in each of sample compositions of Test Examples 1 to 13shown in Tables 1 to 3 was forcedly introduced into the combustionchamber through a fuel injector, and a fuel oil was replaced in thesample and combusted. Since a lubricant base oil is high in viscosity ascompared with the fuel oil, it is difficult to spray a lubricating oilcomposition by a fuel injector. Thus, an additive was mixed in PRF50that is a fuel oil having an octane number of 50 in place of thelubricant base oil, thereby preparing the sample prepared by blending ineach of sample compositions of Test Examples 1 to 13 shown in Tables 1to 3.

An amount of the lubricating oil composition which invades into thecombustion chamber from a crank chamber due to oil loss through pistonis not constant but is largely dominated by the probability. On theoccasion when a large amount of the lubricating oil compositionaccidentally invades into the combustion chamber, and droplets of thelubricating oil composition itself are scattered into the interior ofthe combustion chamber, the influence which the lubricating oilcomposition gives to the combustion becomes maximum. For that reason, byforcedly scattering the droplets having specified properties into theinterior of the combustion chamber to analyze the combustion state, themaximum influence which the composition may give can be evaluated. Then,in the present combustibility test, assuming the case where in alow-tension spark-ignition internal combustion engine, in which a totaltension per cylinder of tensions applied to the piston ring is 100 N orless, and the oil loss through piston is liable to be generated, a largeamount of the lubricating oil composition accidentally invaded into thecombustion chamber, as described above, the sample was forcedlyintroduced into the combustion chamber.

It is to be noted that in the spark-ignition internal combustion engineused for the combustibility test, a general lubricating oil compositionis filled in the crank chamber and the like; however, since the invasionof the lubricating oil composition from the crank chamber into thecombustion chamber is restricted, it is not necessary to consider theinfluence against the results of the present test.

In view of the fact that both the lubricant base oil and the fuel oilare a hydrocarbon, it may be considered that a difference in reactivitywith the additive is small and that the influence which droplets of afuel oil containing a certain concentration of an organic metal-basedadditive give to the combustion is close to that in the case wheredroplets of a lubricant base oil containing the foregoing additive arescattered within the combustion chamber. For that reason, as a result ofthe test, so far as the fuel oil containing a predetermined additivedoes not influence the combustion, even in the case where thelubricating oil composition similarly containing the foregoingpredetermined additive invaded into the combustion chamber, it may bejudged that the combustion is not influenced. Conversely, so far as thecombustion is influenced, when the lubricating oil composition invadesinto the combustion chamber in the actual equipment, it may be judgedthat there is a possibility that the combustion is influenced.

The comprehensive evaluation was made according to the followingcriteria. In the case where the evaluation is A or B, the generationtiming of a cool flame is equal or close to the timing of usual sparkdischarge, and the value of pressure vibration is low, and hence, it maybe said that the deterioration of the combustion state was inhibited,and the knocking was inhibited. On the other hand, in the case where theevaluation is C, the generation timing of a flame is faster than thetiming of usual spark discharge, and the value of pressure vibration ishigh, and hence, it may be said that the combustion state wasdeteriorated, and the knocking was promoted.

<Criteria of Comprehensive Evaluation>

A: As compared with a standard sample, the generation timing of a coolflame is not accelerated, and an increase of the pressure vibration is0.04 or less in terms of a ratio to the standard.B: As compared with a standard sample, the generation timing of a coolflame is accelerated, but an increase of the pressure vibration is 0.04or less in terms of a ratio to the standard.C: As compared with a standard sample, the generation timing of a coolflame is accelerated, and an increase of the pressure vibration is morethan 0.04 in terms of a ratio to the standard.

TABLE 1 Test Example 1 2 3 4 5 Sample Fuel oil — Whole amount RemainderRemainder Remainder Remainder composition Component (A) % by volume — —— — — Component (B1) % by volume — 0.70 0.35 0.18 0.04 Component (B2) %by volume — — — — — Characteristic Component (A) % by mass (Ca) — — — —— values Component (B1) % by mass (Na) — 0.21 0.11 0.05 0.01 Component(B2) % by mass (Mg) — — — — — Measurement Acceleration of generationtiming Standard No No No No results of cool flame Pressure vibration[MPa] 0.016  0.014  0.027  0.013  0.009 Comprehensive evaluation A A A AA

TABLE 2 Test Example 6 7 8 9 10 Sample Fuel oil — Whole amount RemainderRemainder Remainder Remainder composition Component (A) % by volume — —— — — Component (B1) % by volume — — — — — Component (B2) % by volume —2.25 1.50 0.33 0.08 Characteristic Component (A) % by mass (Ca) — — — —— values Component (B1) % by mass (Na) — — — — — Component (B2) % bymass (Mg) — 0.33 0.22 0.06 0.01 Measurement Acceleration of generationtiming Standard Yes Yes No No results of cool flame Pressure vibration[MPa] 0.022  0.183  0.114  0.055  0.024 Comprehensive evaluation A C C AA

TABLE 3 Test Example 11 12 13 Sample Fuel oil — Whole RemainderRemainder composition amount Component (A) % by volume — 2.0 1.0Component (B1) % by volume — — — Component (B2) % by volume — — —Characteristic Component (A) % by mass (Ca) — 0.22 0.11 values Component(B1) % by mass (Na) — — — Component (B2) % by mass (Mg) — — —Measurement Acceleration of generation timing of cool flame Standard YesYes results Pressure vibration [MPa] 0.017 0.061 0.024 Comprehensiveevaluation A C B

It is to be noted that the various additives used are as follows.

Fuel Oil:

Mixture of equal parts of normal-heptane and isooctane (PRF50)

Component (A):

Calcium-based detergent: Ca salicylate (Ca content: 7.8% by mass, basenumber: 225 mgKOH/g)

Component (B1):

Sodium-based detergent: Na sulfonate (Na content: 16.3% by mass, basenumber: 460 mgKOH/g)

Component (B2):

Magnesium-based detergent: Mg salicylate (Mg content: 6.9% by mass, basenumber: 300 mgKOH/g)

From the results of Table 1, it is understood that in the sodium-basedadditive (B1), when its content as expressed in terms of a sodium atomis 0.21% by mass or less, the generation timing of the cool flame is notaccelerated, and the increase of the pressure vibration is suppressed.From the results of Table 2, it is understood that in themagnesium-based additive (B2), when its content as expressed in terms ofa magnesium atom is less than 0.22% by mass, the generation timing ofthe cool flame is not accelerated, and the increase of the pressurevibration is suppressed. In addition, from the results of Table 3, it isunderstood that in the calcium-based detergent (A), when its content asexpressed in terms of a calcium atom is less than 0.22% by mass, thoughthe generation timing of the cool flame is accelerated, the increase ofthe pressure vibration is suppressed. From these results, it isunderstood that when the contents of the component (A), the component(B1), and the component (B2) in the lubricating oil composition are setto the aforementioned ranges, respectively, the deterioration of thecombustion state of the spark-ignition internal combustion engine may beprevented.

(Hot Tube Test (at 280° C.))

The hot tube test was carried out by setting a test temperature to 280°C. and a test time to 16 hours and making other conditions in conformitywith those of JPI-5S-55-99. Conforming to JPI-5S-55-99, a lacquerattached to a test tube after the test was evaluated between Point 0(black) and Point 10 (colorless) and evaluated at every 0.5 point. It ismeant that as the numerical value is large, a deposit is less, and thedetergency is favorable. As for the grade point, though Points 7 or moreare evaluated to be acceptable.

TABLE 4 Example 1 2 3 4 5 Composition Base oil — Remainder RemainderRemainder Remainder Remainder Component (A) % by mass 1.8 1.8 1.8 1.81.8 Component (B1) % by mass 0.3 — — — — Component (B2) % by mass — 0.70.7 0.7 0.7 Component 1 (C) % by mass 0.5 0.5 0.2 — — Component 2 (C) %by mass — — — 0.9 — Component 3 (C) % by mass — — — — 0.5 Component 4(C) % by mass — — — — — Component 5 (C) % by mass — — — — — Component(D) % by mass 0.7 0.7 0.7 0.7 0.7 Dispersant 1 % by mass 2.5 2.5 2.5 2.52.5 Dispersant 2 % by mass 2.0 2.0 2.0 2.0 2.0 Anti-wear agent % by mass1.1 1.1 1.1 1.1 1.1 Viscosity Index improver % by mass Adjusted*²Adjusted*² Adjusted*² Adjusted*² Adjusted*² Other additives % by mass2.0 2.0 2.0 2.0 2.0 Properties/ Component (A) % by mass (Ca) 0.14 0.140.14 0.14 0.14 evaluation Component (B1) % by mass (Na) 0.05 — — — —Component (B2) % by mass (Mg) — 0.05 0.05 0.05 0.05 Component (C) % bymass (S) 0.15 0.15 0.05 0.05 0.05 (Mg + Na)/Ca*¹ 0.36 0.36 0.36 0.360.36 HTHS viscosity at 150° C. (mPa · s) 2.3 2.3 2.3 2.3 2.3 Kinematicviscosity at 100° C. (mm²/s) 7.2 7.3 7.2 7.3 7.3 Kinematic viscosity at40° C. (mm²/s) 30.2 30.8 30.5 30.6 31.1 Sulfated ash content (% by mass)0.9 0.9 0.9 0.9 0.9 NOACK volalite loss (%) 14 14 14 14 14 Hot tube test(point) 10 8 7.5 7 7 Example Comparative Example 6 7 8 1 2 CompositionBase oil — Remainder Remainder Remainder Remainder Remainder Component(A) % by mass 1.8 1.8 1.8 1.8 1.8 Component (B1) % by mass — — — — —Component (B2) % by mass 0.7 0.7 0.7 0.7 — Component 1 (C) % by mass — —— — — Component 2 (C) % by mass — — — — 0.9 Component 3 (C) % by mass —— — — — Component 4 (C) % by mass 0.8 — — — — Component 5 (C) % by mass— 0.6 1.7 — — Component (D) % by mass 0.7 0.7 0.7 0.7 0.7 Dispersant 1 %by mass 2.5 2.5 2.5 2.5 2.5 Dispersant 2 % by mass 2.0 2.0 2.0 2.0 2.0Anti-wear agent % by mass 1.1 1.1 1.1 1.1 1.1 Viscosity Index improver %by mass Adjusted*² Adjusted*² Adjusted*² Adjusted*² Adjusted*² Otheradditives % by mass 2.0 2.0 2.0 2.0 2.0 Properties/ Component (A) % bymass (Ca) 0.14 0.14 0.14 0.14 0.14 evaluation Component (B1) % by mass(Na) — — — — — Component (B2) % by mass (Mg) 0.05 0.05 0.05 0.05 —Component (C) % by mass (S) 0.05 0.05 0.15 — 0.05 (Mg + Na)/Ca*¹ 0.360.36 0.36 0.36 — HTHS viscosity at 150° C. (mPa · s) 2.3 2.3 2.3 2.3 2.3Kinematic viscosity at 100° C. (mm²/s) 7.3 7.2 7.2 7.2 7.1 Kinematicviscosity at 40° C. (mm²/s) 31.2 30.6 31.1 30.5 29.9 Sulfated ashcontent (% by mass) 0.9 0.9 0.9 0.9 0.7 NOACK volalite loss (%) 14 14 1414 14 Hot tube test (point) 7 7 8 6 6.5

In the table, the terms “% by mass (Ca)”, “% by mass (Na)”, “% by mass(Mg)”, and “% by mass (S)” are the contents as expressed in terms of acalcium (Ca) atom, a sodium (Na) atom, a magnesium (Mg) atom, and asulfur (S) atom, respectively on a basis of the total amount of thelubricating oil composition.

1: A mass ratio of the magnesium atom (Mg) and/or the sodium atom (Na)to the calcium atom (Ca) [(Mg and/or Na)/Ca]

2: Adjusted to the amount at which the HTHS viscosity at 150° C. was 2.3mPa·s

The various additives used are as follows.

Base Oil:

Paraffin-based mineral oil (kinematic viscosity at 100° C.: 4.1 mm²/s,kinematic viscosity at 40° C.: 17.8 mm²/s, viscosity index: 134)

Component (A):

Calcium-based detergent: Ca salicylate (Ca content: 7.8% by mass, basenumber: 225 mgKOH/g)

Component (B1):

Sodium-based detergent: Na sulfonate (Na content: 16.3% by mass, basenumber: 460 mgKOH/g)

Compound (B2):

Magnesium-based detergent: Mg salicylate (Mg content: 6.9% by mass, basenumber: 320 mgKOH/g)

Component 1 (C):

Dialkyl dithiocarbamate (sulfur content: 30.3% by mass, nitrogencontent: 6.6% by mass)

Component 2 (C):

Dialkyl thiodipropionate (sulfur content: 5.6% by mass)

Component 3 (C):

Sulfur-containing phenol (sulfur content: 11.0% by mass)

Component 4 (C):

Hydroxybenzyl sulfide (sulfur content: 6.8% by mass)

Component 5 (C):

Benzothiazole (sulfur content: 8.9% by mass, nitrogen content: 4.7% bymass)

Component (D):

Molybdenum dithiocarbamate (MoDTC, Mo content: 10% by mass)

Dispersant 1:

Polymeric alkenyl succinimide (base number: 24 mgKOH/g, nitrogencontent: 1% by mass)

Dispersant 2:

Boronated alkenyl succinimide (base number: 25 mgKOH/g, boron content:1.3% by mass)

Anti-Wear Agent:

Zinc dithiophosphate (zinc content: 8.9% by mass, phosphorus content:7.4% by mass, sulfur content: 15.0% by mass)

Viscosity Index Improver:

Polymethacrylate (PMA, Mw=510,000, resin concentration: 19% by mass)

Other Additives:

Diphenylamine, alkylphenol, copper deactivator, silicone-based defoamingagent, and polymethacrylate-based pour point depressant

From the aforementioned Tables 1 to 3, it was confirmed that even if theoil loss through piston is generated, even at the highest estimate, evenin the case where the additives are contained in the quantities shown inTables 1 to 3 in the combustion chamber of the cylinder, thedeterioration of the combustion state does not take place. In view ofthis fact, the lubricating oil compositions shown in Table 4 wereprepared as the composition in which the deterioration of the combustionstate does not take place.

According to the lubricating oil compositions of Examples 1 to 8 asshown in Table 4, it was confirmed that the lubricating oil compositionsin which the calcium-based detergent (A), the sodium additive (B1)and/or the magnesium additive (B2), and the various ash-freesulfur-based additives (C) are blended in the predetermined blendingratios have excellent detergency, and that from the results of Tables 1to 3, they have an excellent effect for preventing the deterioration ofthe combustion state of the spark-ignition internal combustion engine.

On the other hand, it was confirmed that the lubricating oil compositionof Comparative Example 1 not containing the ash-free sulfur-basedadditive (C) and the lubricating oil composition of Comparative Example2 containing the ash-free sulfur-based additive (C) but not containingthe sodium additive (B1) and the magnesium additive (B2) were inferiorin detergency. In addition, from comparison of the Examples withComparative Example 1 (in particular, comparison of Example 2 withComparative Example 1), an effect that by using a combination of theash-free sulfur-based additive (C) with the calcium-based detergent andthe sodium additive (B1) and/or the magnesium additive (B2), thedetergency is more improved was confirmed.

REFERENCE SIGNS LIST

-   -   1: Spark-ignition internal combustion engine    -   11: Cylinder block    -   12: Piston crank mechanism    -   13: Valve mechanism    -   21: Cylinder    -   22: Crank case    -   23: Piston    -   24: Crank shaft    -   30: Piston ring    -   31: Top ring    -   32: Second ring    -   33: Oil ring    -   41: Oil pan    -   C: Combustion chamber    -   F: Spark plug    -   L: Lubricating oil composition

1: A lubricating oil composition, comprising: a base oil; (A) acalcium-based detergent; (B) at least one of (B1) a sodium-basedadditive and (B2) a magnesium-based additive; and (C) an ash-freesulfur-based additive, wherein: a content of the calcium-based detergent(A) as expressed in terms of a calcium atom content is 0.15% by mass orless on a basis of a total amount of the lubricating oil composition; asum total of a content of the sodium-based additive (B1), as expressedin terms of a sodium atom content, and a content of the magnesium-basedadditive (B2), as expressed in terms of a magnesium atom content, is0.2% by mass or less on a basis of the total amount of the lubricatingoil composition; and a content of the ash-free sulfur-based additive (C)as expressed in terms of a sulfur atom content is 0.01% by mass or moreon a basis of the total amount of the lubricating oil composition. 2:The lubricating oil composition according to claim 1, wherein a NOACKvolatile loss of the lubricating oil composition is 10% by mass or more.3: The lubricating oil composition according to claim 1, wherein thecalcium-based detergent (A) is a calcium-based detergent having a basenumber of 10 to 600 mgKOH/g. 4: The lubricating oil compositionaccording to claim 1, wherein the sodium-based additive (B1) is asodium-based detergent having a base number of 10 to 600 mgKOH/g. 5: Thelubricating oil composition according to claim 1, wherein themagnesium-based additive (B2) is a magnesium-based detergent having abase number of 10 to 600 mgKOH/g. 6: The lubricating oil compositionaccording to claim 1, further comprising: (D) an organicmolybdenum-based additive, wherein a content of the molybdenum-basedadditive (D) is 0.005 to 0.20% by mass as expressed in terms of amolybdenum atom content on a basis of the total amount of thelubricating oil composition. 7: The lubricating oil compositionaccording to claim 1, which has a sulfated ash content of 1.0% by massor less on a basis of the total amount of the composition. 8: Thelubricating oil composition according to claim 1, wherein: the contentof the calcium-based detergent (A) as expressed in terms of a calciumatom content is from 0.05 to 0.15% by mass on the basis of the totalamount of the lubricating oil composition; and a mass ratio of themagnesium atom (Mg), the sodium atom (Na), or both, to the calcium atom(Ca) is from 0.03 to 3.5. 9: The lubricating oil composition accordingto claim 1, further comprising: at least one additive for lubricatingoil selected from the group consisting of a viscosity index improver, adispersant, an anti-wear agent, an extreme pressure agent, anon-sulfur-based antioxidant, and a defoaming agent. 10: The lubricatingoil composition according to claim 1, wherein the lubricating oilcomposition is adapted to function as a lubricating oil composition fora spark-ignition internal combustion gasoline engine. 11: A method forproducing a lubricating oil composition, the method comprising: blendinga base oil with (A) a calcium-based detergent, (B) at least one of (B1)a sodium-based additive and (B2) a magnesium-based additive, and (C) anash-free sulfur-based additive, in such a manner that: a content of thecalcium-based detergent (A) as expressed in terms of a calcium atomcontent is 0.15% by mass or less on a basis of a total amount of thelubricating oil composition; a sum total of a content of thesodium-based additive (B1), as expressed in terms of a sodium atomcontent, and a content of the magnesium-based additive (B2), asexpressed in terms of a magnesium atom content, is 0.2% by mass or lesson a basis of the total amount of the lubricating oil composition; and acontent of the ash-free sulfur-based additive (C) as expressed in termsof a sulfur atom content is 0.01% by mass or more on a basis of thetotal amount of the lubricating oil composition. 12: A spark-ignitioninternal combustion engine in which a total tension per piston oftensions applied to the piston ring is 100 N or less, the spark-ignitioninternal combustion engine comprising a lubricating oil composition,said composition comprising: a base oil; (A) a calcium-based detergent;(B) at least one of (B1) a sodium-based additive and (B2) amagnesium-based additive; and (C) an ash-free sulfur-based additive,wherein: a content of the calcium-based detergent (A) as expressed interms of a calcium atom content is 0.15% by mass or less on a basis of atotal amount of the lubricating oil composition; a sum total of acontent of the sodium-based additive (B1), as expressed in terms of asodium atom content, and a content of the magnesium-based additive (B2),as expressed in terms of a magnesium atom content, is 0.2% by mass orless on a basis of the total amount of the lubricating oil composition;and a content of the ash-free sulfur-based additive (C) as expressed interms of a sulfur atom content is 0.01% by mass or more on a basis ofthe total amount of the lubricating oil composition. 13: A method forlubricating a spark-ignition internal combustion engine, the methodcomprising lubricating the spark-ignition internal combustion enginewith a lubricating oil composition comprising: a base oil; (A) acalcium-based detergent; (B) at least one of (B1) a sodium-basedadditive and (B2) a magnesium-based additive; and (C) an ash-freesulfur-based additive, wherein: a content of the calcium-based detergent(A) as expressed in terms of a calcium atom content is 0.15% by mass orless on a basis of a total amount of the lubricating oil composition; asum total of a content of the sodium-based additive (B1), as expressedin terms of a sodium atom content, and a content of the magnesium-basedadditive (B2), as expressed in terms of a magnesium atom content, is0.2% by mass or less on a basis of the total amount of the lubricatingoil composition; and a content of the ash-free sulfur-based additive (C)as expressed in terms of a sulfur atom content is 0.01% by mass or moreon a basis of the total amount of the lubricating oil composition. 14:The lubricating oil composition of claim 1, which is adapted to functionas a lubricating oil composition for a spark-ignition internalcombustion engine in which a total tension per piston of tensionsapplied to the piston ring is 100 N or less.